The radio communication system disclosed in a patent document 1 (i.e., Japanese Patent Laid-Open No. 2003-244018) includes a communication radio, such as a burst modem, and an antenna side device, such as an outdoor device, for performing amplification, etc., at the time of transmission and reception positioned at distant positions from each other. The communication radio and the antenna side device are connected by a single coaxial cable. Through the coaxial cable, a transmission signal is sent to the antenna side device from the communication radio and a reception signal is sent to the communication radio from the antenna side device.
In addition, a signal detection circuit is provided in the antenna side device. When the level of a transmission signal is higher than a threshold, a transmission amplifier is connected to an antenna. When the level of a transmission signal is equal to or lower than the threshold, a reception amplifier is connected to the antenna. In such configuration, the switching of amplifiers, that is, between the transmission amplifier and the reception amplifier at the time of switching between signal transmission and signal reception, is performed only with the single coaxial cable that is used for both transmission and reception of the signal.
In the above-described configuration for the switching of amplifiers based on the level of the transmission signal, a certain period of time is required between the rise of the level of the transmission signal and a desired amplification of the signal because time is required for the switching of a switch that switches amplifiers and a starting of the transmission amplifier. Therefore, a front portion (i.e., front edge) of a waveform of the transmission signal may be dropped or deformed. In other words, the waveform may be deteriorated. If the degree of such waveform deformation is severe, the receiving side may not be capable of demodulating the transmission signal.